1. Field of the Invention
Aspects of the invention relate generally to data communication over Internet Protocol (IP) communication systems, and more particularly to characterizing the performance of error correction of data communication over IP communication systems.
2. Description of the Prior Art
Previously, digital video transmission over networks has been accomplished by way of dedicated, private connections involving Asynchronous Transfer Mode and similar methods to help guarantee a desired Quality of Service (QoS). More specifically, private or dedicated networks often provide the low packet loss and limited latency desired for streaming video transmissions.
However, private networks dedicated for video communication tend to be expensive to configure and operate. As a result, many organizations have migrated to the use of Internet Protocol (IP) networks for their digital video transmission needs. While costs are reduced as a result, IP networks typically are not designed with the goal of maintaining a QoS acceptable for video data. Packet loss, latency, jitter and other maladies associated with IP networks often wreak havoc with digital video transmission over IP.
To counteract at least some of these problems, video transmissions often employ a forward error correction (FEC) scheme to reduce the amount of packet loss. FIG. 1 provides a simplified block diagram of a video transmission system 1 employing FEC. The system 1 includes a video encoder 2, an FEC encoder 4, an IP network 6, an FEC decoder 8, and a video decoder 10. The video encoder 2 encodes a digital video input signal 12 into a digital video packet stream compatible with the IP network 6. In some cases, the digital video packet stream complies with one of the Motion Picture Experts Group (MPEG) standards, such as the MPEG-2 Transport Stream (TS) format. Further, the video encoder 2 encapsulates the MPEG-2 TS packets within an IP packet stream for transfer over the IP network 6. Typically, the IP packet stream is embodied as a Real-time Transport Protocol (RTP) over IP packet stream, or a User Datagram Protocol (UDP) over IP packet stream.
The FEC encoder 4 then generates one or more IP packets providing data redundancy for error correction of the IP packets containing the digital video packets. More specifically, the error correction IP packets are typically generated from the data in the digital video packets according to a mathematical algorithm, and then subsequently used in conjunction with a companion algorithm to correct errors in the digital video packets. One example of forward error correction for video data is discussed in “Pro-MPEG Code of Practice #3, Release 2” (2004), provided by the Pro-MPEG Forum, incorporated herein by reference in its entirety. The IP packets carrying the digital video data stream packets, as well as the error correction IP packets, are then transferred over the IP network 6 to a destination.
At the destination, the FEC decoder 8 decodes the error correction IP packets in accordance with the error correction scheme to correct errors in the IF packets carrying the digital video packet stream. The IP packets of the corrected digital video packet stream are then forwarded to the video decoder 10, which decodes the digital video packet stream to produce an output video signal 14.
Many different error correction schemes are available for video transport. Thus, the ability to characterize the performance of one of more of the error correction schemes under a variety of operating conditions, especially with respect to random loss protection, would be advantageous for selecting a scheme appropriate for the particular application involved. Unfortunately, most testing equipment available for monitoring IP packets are only connectable within the destination at the input to the FEC decoder 8, and thus are not positioned to measure the performance of the IP error correction scheme after the IP packets have been corrected. Also, most video decoders 10 receive IP packets as input, but produce MPEG-2 TS packets at one of its outputs, thus prohibiting analysis of the effectiveness of the IP error correction scheme at that point.